Phytoremediation Potential of Jack Bean Plant for Multi-Element Contaminated Soils From Ribeira Valley, Brazil

Soil contamination with metal(oid)s is of concern due to deleterious effects on ecosystems, plants and human health. This study aims at determining the potential of jack bean, Canavalia ensiformis, to be used as phytoremediator of soils contaminated with Pb, Zn, and As from past mining activities in the Ribeira Valley, Brazil. A pot experiment is conducted using soils collected from two areas contaminated with different concentrations of Pb, As, and Zn. Only in the most contaminated soil, elemental concentrations are above the limit established for agricultural purposes by Brazilian regulatory agencies. Plant tolerance is evaluated in terms of growth, elemental accumulation, establishment of root symbiosis, and biochemical indicators of metal toxicity. Plants are able to produce high biomass without signs of oxidative stress. The content of free amino acids in leaves increases when plants grown in the soil with higher metal(oid) concentrations indicating changes in physiology. Mycorrhizal symbiosis is established; however, nodulation with native rhizobia is strongly inhibited in the most contaminated soil. Jack bean roots act as a barrier to translocation retaining most of the absorbed metals, especially for Pb. The translocation index for Zn and As is higher than for Pb. In conclusion, jack bean plant can be considered of interest for phytostabilization of multi-element contaminated soils due to its high capacity for immobilizing potentially toxic elements in roots. Although Zn and As are more mobile and accumulate in concentration levels above phytotoxicity thresholds, C. ensiformis is a tolerant species.